The 4′-azido cytidine of formula I has been disclosed by Maag et al. (J. Med. Chem. 1992 35:1440) and by R. R. Devos et al (WO 02/100415). Synthetic pathways for its preparation have been described in the PCT Publication WO 2004/046159 A1 and WO 2005/000864 A1.
For the transformation of the intermediate 4′-azido-triacyl uridine into the desired 4′-azido-cytidine it was suggested to run the reaction in the presence of triazole, phosphorous oxychloride and triethylamine. However it was found that the use of triazole is not favorable on a technical scale process due to its low biodegradability. The object of the present invention therefore was to provide a process which can be performed on a technical scale and which is not suffering from the disadvantages as outlined above.